Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism

Summary

After a 5 week conditioning period on a recumbent cycle, The High Intensity Interval Training (HIIT) group perform sprints while the Endurance Training (ET) group performed a more traditional aerobic protocol, throughout the remaining 15 weeks. Both groups progressed in intensity. At the conclusion of the study, the HIIT group lost over 3 times as much subcutaneous fat as the ET group despite expending less than half as many calories. For every calorie expended during HIIT, there was a nine fold loss of subcutaneous body fat, as compared to the ET group.

Comparison

(20 week program, 17 subjects)

Mode (ergocycle)	Endurance Training	High Intensity Interval Training
Duration (minutes)	30 and increased to 45	30
Frequency	4/wk and increased to 5/wk	25 continuous sessions; half completed before week 5 Week 5-20: 19 long & 16 short interval sessions
Intensity	60% HRR and increased to 85% HRR	70% HRR warmup 60% of max output in 10 seconds & 70% of max output in 90 seconds; increasing 5% every 3 weeks
Energy Expended (MJ)	120.4 ± 31.0	57.9 ± 14.4
Fat Loss (mm)	4.5	13.9

HIIT Protocol

• High Intensity Interval Training (HIIT)
  • 5 minute warm-up at 50% HRR
  • Short-interval work
    • Initially 10 and later 15 bouts
    • 15 seconds increasing to 30 seconds
  • Long-interval
    • 4 to 5 bouts
    • 60 seconds increasing to 90 seconds
  • Bouts separated by recovery periods allowing heart rate to return to 120 to 130 bpm
    • Creatine phosphate recovery may take 4 minutes to replete beteem maximal bouts

Dependant Variables

• Fat Loss measured in millimeters
  • Difference of before and after sum of skin fold measurements
  • Sum of skin folds
    • Triceps, Biceps, Calf, Subscapular, Suprailiac, Abdomen

Also 3-hydroxyacyl coenzyme A dehydrogenase (HADH) enzyme activity, a marker of the activity of beta-oxidation, was significantly greater after the HIIT program

Also see SIT Guidelines and Sample Programs.